1. Field of the Invention
The present invention relates generally to specimen inspection and review. More particularly, the present invention relates to e-beam inspection and systems.
2. Description of the Background Art
Automated inspection and review systems are important in process control and yield management for the semiconductor and related microelectronics industries.
An example of an electron beam (e-beam) tool for an inspection or review system is shown in FIG. 1 for purposes of background explanation. The secondary electron emission microscope (SEEM) apparatus of FIG. 1 is a projection type system, where a large spot of electrons rather than a small one is formed at the surface of the specimen, and the secondary electrons from this spot are imaged onto a two-dimensional detector. Typically, the specimen may comprise a semiconductor wafer having integrated circuit related structures formed on its surface. Alternatively, the specimen may be another type of sample.
The system of FIG. 1 is described in U.S. Pat. No. 5,973,323, entitled xe2x80x9cApparatus and Method for Secondary Electron Emission Microscope,xe2x80x9d inventors Adler et al., and assigned at issuance to KLA-Tencor Corporation of San Jose, Calif. The disclosure of U.S. Pat. No. 5,973,323 is hereby incorporated by reference. As described in that patent, FIG. 1 shows the basic configuration for the Secondary Electron Emission Microscopy (SEEM) apparatus. An electron gun source 10 emits a beam 11 of primary electrons e1 along path 12. The electron beam 11 is collimated by electron lens 13 and continues along path 12. Magnetic beam separator 14 then bends the collimated electron beam 11 to be incident along electron optical axis OA normal to the surface to be inspected. Objective electron lens 15 focuses the primary electrons, e1, into a beam having a spot size typically in the range 1-10 mm and an incident energy on the order of 1 keV on specimen 9.
Primary electrons e1 incident on the specimen 9 produce secondary electrons e2 which travel back along the axis OA perpendicular to the inspection surface to objective electron lens 15, where they are re-collimated. Magnetic beam separator 14 bends the electrons to travel along image path 16. The electron beam along image path 16 is focused by projection electron lens 17 to image plane 18, where there is an electron detector 19, which is a camera or preferably a time delay integrating (TDI) electron detector. The operation of an analogous TDI optical detector is disclosed in U.S. Pat. No. 4,877,326, entitled xe2x80x9cMethod and Apparatus for Optical Inspection of Substrates,xe2x80x9d inventors Chadwick et al., and assigned at issuance to KLA Instruments Corporation. The disclosure of U.S. Pat. No. 4,877,326 is incorporated herein by reference. The image information may be processed directly from a xe2x80x98back thinxe2x80x99 TDI electron detector 19, or the electron beam may be converted into a light beam and detected with an optional optical system 20 and a TDI optical detector.
Despite advances in e-beam inspection and review, such as SEEM described above, further improvement may be made. For example, it is typically desirable to increase the resolution of an inspection or review system. Resolution may be defined as the smallest distance apart that two point may be distinguishable as separate points. Current e-beam inspection and review systems have resolutions of about 100 nanometers (0.1 micrometers). Generally, the higher the resolution, the smaller the defects that may be detected and characterized by the automated inspection and review systems. In other words, the resolution of an e-beam system limits the smallness of the features that may be detected and characterized. Hence, in order to detect and characterize smaller and smaller features on semiconductors and other specimens, it is desirable to increase the achievable resolution of the system.